Removal of ammonia from fluids

ABSTRACT

A method and equipment for removing ammonia from effluent, flue or waste fluids that include oxygen. The method includes at least the following stages: Part of the fluid ( 1 ) is conveyed to a decomposition/oxidation unit ( 2 ) and part of the fluid ( 1 ) is conveyed to a by-pass unit ( 3 ); part of the fluid ( 1 ) including ammonia is oxidized in the decomposition/oxidation unit ( 2 ) of ammonia; the fluid ( 1 H) that was oxidized in the decomposition/oxidation unit ( 2 ) and the fluid ( 1 ) that was conveyed to the by-pass unit are mixed in a mixing unit ( 4 ) to form a fluid mixture ( 1 S), and the fluid mixture ( 1 S) is conveyed to a selective reduction unit ( 5 ).

BACKGROUND OF THE TECHNOLOGY

The object of the invention is a method and equipment for the removal ofammonia from oxygen-comprising fluids, such as effluent, flue or wastefluids. Another object of the invention is equipment suitable to thismethod.

Ammonia (NH₃) can be generated in various conditions or it is used as areactant in some processes. Ammonia that has escaped into the air or thesurface waters is harmful to humans and the environment; therefore, itis not allowed to escape in considerable amounts along with effluentgases from the processes. The authorities have set the highest allowablecontents or total emission amounts for ammonia emissions. Ammonia isalso used for the adjustment of pH in solutions. The effluent gases ofprocesses may comprise small or large amounts of ammonia. Urea- orNH₃-SCR is a common removal method of nitrogen oxides, which can releasesmall amounts of ammonia. Ammonia is also generated from nitrogencompounds in low-oxygen conditions, such as stoichiometric or richcombustion mixtures, where the fuels are solid, liquid or gaseous.Ammonia can be generated in fuel refining. Ammonia can be generated, forexample, when purifying soil, other solid materials or liquids thatcomprise ammonia as a chemical or derivatives of ammonia, or it can begenerated naturally in low-oxygen conditions. In agriculture, largeamounts of ammonia emissions are generated. When gasifying fuels,ammonia can also be generated together with HCN from the nitrogencontained in the fuel.

For the removal of ammonia from gases or liquids, catalyticdecomposition, adsorption, absorption or thermal decomposition methodshave been used. In reductive conditions, NH₃ decomposes or reactsthermally or catalytically, forming mainly nitrogen (N₂) and smallamounts of laughing gas (N₂O). In mixtures comprising excess amounts ofoxygen, NH₃ can form nitrogen oxides (NO, NO₂, N₂O) in the thermal orcatalytic methods, and the selectivity to nitrogen is a critical factor.The formation of laughing gas is also higher than in reductive orstoichiometric conditions.

In the catalytic decomposition of ammonia, two different operatingconditions can definitely be distinguished, i.e., decomposition in arich mixture (low amounts of oxygen) or a lean mixture (excessiveamounts of oxygen). When there are excessive amounts of oxygen, the mainreaction is often that of NH₃ into nitrogen oxides, and the selectivityto nitrogen is a problem. When there are low amounts of oxygen, nitrogenoxides are not easily generated but the oxygen required must be obtainedselectively before carbon monoxide, hydrocarbons or hydrogen, and theoxygen supply is limited. The decomposition of NH₃ at high temperaturesand pressures is thermodynamically limited. Ammonia has been decomposedby alumina-based Ni, Ru catalysts (Mojtahedi et al., Fuel Proc. Tech. 45(1995) 221). For the removal of nitrogen compounds from gasifying gases,a mixture formed by the oxide of the metals (such as Fe oxide) of thefourth cycle of the group VIII of the periodic system and alkali metalor alkali earth metal carbonate or oxide (such as CaO) (FI 904697,Leppälahti and Simell) have been used. Generally, Mo, W, Re, Fe, Co, Rh,Ni, Pt, Cu and V (Catal. Sci. Tech.1 (1981) 118, or U.S. Pat. No.5,055,282) have been mentioned to be the chemical elements that aresuitable to the decomposition of NH3 in the catalyst. It has beenobserved that Ru/alumina decomposes NH3 at a temperature of as low as500° C. (U.S. Pat. No. 5,055,282). The Ru/alumina catalyst may also haveincluded various alkali metals and alkali earth metals (K, Li, Na, Cs,Ca, Ba, Mg). The decomposition of ammonia has also been exploited in theindustrial processing of steel products.

Selective catalytic oxidation (SCO) refers to a method, wherein NH₃ isselectively oxidized into nitrogen (N₂) with oxygen. This method relatesto a phased air supply in combustion or by gasifying, wherein theoxidation of NH₃ into NO_(x) can be prevented. There are difficulties inpreventing the formation of NO_(x) and the integration of the methodinto the combustion/gasifying process in question. The catalysts usedincluded MoO₃, V₂O₅, Bi₂O₃, and PbO, MoO₃/SiO₂ catalysts (Boer et al.Stud. Surf. Sci. Catal. 72 (1992) 133). The poor activity, selectivityor durability of the catalysts are typical problems, especially, whenthe operating temperatures are normally high (>400° C.).

GENERAL DESCRIPTION OF THE INVENTION

The purpose of the invention is to provide a catalytic method andequipment for objects comprising ammonia, which can be used toselectively remove NH₃ from fluids into nitrogen. The method and theequipment are suitable for the treatment of effluent, flue, and wastefluids, in particular.

The invention is based on the fact that an NH₃-bearing fluid mixture isconveyed through two functional units, where the NH₃ effluents can beconverted into nitrogen at a high selectivity. First, NH₃ is decomposedinto nitrogen and partly converted catalytically or thermally intonitrogen oxides NO and NO₂ in the oxidation/decomposition unit of NH₃,through which all of the fluid goes, or part of the fluid can bypassthis unit through a by-pass. After the by-pass, these fluid streamscombine and are allowed to mix together in a mixing space, where thefluids comprising NH₃ and nitrogen oxides mix well with each other. Themixture thus obtained is conveyed to a selective reduction unit, whereNH₃ and the nitrogen oxides react with each other catalytically orthermally, mainly forming selectively nitrogen N₂, which is the maincomponent of the fluid coming out. In the oxidation/decomposition unitof NH₃, there can be one or more oxidation catalysts of NO or NH₃ ordecomposition catalysts of NH₃, and in the selective reduction unit, oneor more SCR catalysts, which catalysts can have the same or differentcompositions. Before and after the SCR unit, there can also be a removalunit of laughing gas, where the laughing gas that is forming or going inis decomposed or reduced into nitrogen. The removal unit of laughing gascan also be situated immediately after the oxidation/decomposition unitof NH₃ before the by-pass joins the mixture.

The method according to the invention comprises at least the followingstages:

-   -   part of the fluid is conveyed to the decomposition/oxidation        unit and part of the fluid is conveyed to the by-pass unit,    -   part of the fluid comprising ammonia is oxidized in the        decomposition/oxidation unit of ammonia,    -   the fluid that was oxidized in the decomposition/oxidation unit        and the fluid that was conveyed to the by-pass unit are mixed in        the mixing unit to form a fluid mixture, and    -   the fluid mixture is conveyed to the selective reduction unit.

Correspondingly, the equipment comprises at least the following parts:

-   -   a decomposition/oxidation unit for decomposing and oxidizing the        ammonia in the fluid,    -   a by-pass unit for conveying the fluid past the        decomposition/oxidation unit,    -   a mixing unit for mixing the fluid that was oxidized in the        decomposition/oxidation unit and the fluid that was conveyed to        the by-pass unit to form a fluid mixture, and    -   a reduction unit for the selective reducing of the fluid        mixture.

By means of the method according to the invention, it is possible toselectively convert ammonia into nitrogen that is harmless in a widetemperature range, and the amounts of harmful nitrogen oxides (NO, NO₂,N₂O) remain very low. In known methods, the operational windows arenarrow regarding the temperature and the contents, and nitrogen oxidesare usually generated therein as by-products. In thedecomposition/oxidation unit of NH₃, it is possible to decompose part ofthe ammonia into nitrogen and to oxidize part of it into NO/NO₂. Theby-pass makes it possible to adjust the ratio of NH₃/NO_(x) before thereduction unit so that the mixture reacts selectively, forming nitrogen.The mixing units are needed to mix the two fluid flows together.

According to an object of the invention, the fluid mixture is conveyedto the removal unit of laughing gas. This provides the advantage thatthe laughing gas that was generated in the previous units can beremoved. Usually, the formation of laughing gas is a problem in theammonia removal methods.

According to an object of the invention, the ammonia of the fluidmixture is selectively converted into nitrogen N₂ in the selectivereduction unit. The method according to the invention is first used tocreate a suitable mixture, which in the reduction unit reacts, formingnitrogen.

According to an object of the invention, the functional units (thedecomposition/oxidation unit of NH₃, the reduction unit and/or theremoval unit of laughing gas) function thermally or catalytically or bymeans of a combination thereof. The same idea can be applied both tothermal and catalytic reactions. According to an object of theinvention, the decomposition/oxidation unit of ammonia, the selectivereduction unit, and/or the removal unit of laughing gas functioncatalytically and they are coated on the surfaces of cell structuresthat comprise straight, parallel, divergent and/or winding flowchannels, the structures being made of ceramic, metallic or catalyticmaterials.

According to an object of the invention, the method comprises aselective reduction unit and a removal unit of laughing gas, which areintegrated into the same unit. The method is rendered simpler byintegrating the two units together, if possible in the operatingconditions. Even if the units were integrated into one, either one ofthem can also be a separate unit. Some catalysts are capable offunctioning effectively in both reactions, whereby the integration ispossible.

According to an object of the invention, the portion of the by-pass fromthe total fluid flow is 1 to 99.9%, preferably 60 to 99%. In order tomake the method work, a by-pass is needed, the extent of which can varyaccording to the circumstances. With the invention, it was observed thatit is preferable that the by-pass is larger than the volume of flowgoing to the decomposition/oxidation unit of NH₃.

According to an object of the invention, there are one or more flowregulators and/or uncoated cells in the by-pass unit. The flowregulators can be used to regulate the extent of the by-pass accordingto the operating conditions, and to use, for example, for feedbackcoupling to regulate from the concentrations after the reactor. Theuncoated cell gives the advantage that the flow can be controlledwithout separate regulating units. The by-pass can also comprise anempty flow channel with its size selected so that the extent of theby-pass is suitable. By using, in the by-pass, a cell similar to that ofthe decomposition/oxidation unit, the flow distribution remains the sameat different temperatures. If the flow channels were different, theirtemperature dependences would be different and, thus, the flowdistribution would change to some extent as a function of temperature.

According to an object of the invention, in the mixing unit, a fluidmixture comprising ammonia and nitrogen oxides is prepared from thefluid that comprises ammonia. It is essential to mix the two fluidstogether before conveying them to the reduction unit.

According to an object of the invention, the by-pass is adjusted so thatthe ratio of NH₃/NO_(x) contents in the mixing unit is within 0.1 and10, preferably within 0.8 and 1.6. The optimal mixing ratio depends onthe circumstances. In catalytic objects, the mixing ratio value can benear 1, but in thermal applications, in particular, the ratio can behigh.

According to an object of the invention, the method operates with aparallel or reverse flow or a combination thereof. The method can beimplemented as sequential units or as a system that utilizes thereaction heats by means of the reverse flow. It is also possible to usea system, wherein the flow is recycled through part of the units only,e.g., the removal unit of laughing gas can be reversed after the flowsystem, functioning on the principle of flow-through. In this way,energy is recycled in the reaction, where the most heat is generated,but there is no need to place two removal units of laughing gas in thereverse flow reactor. The method is well-suited to the reverse flowreactor, as the reduction unit can be in the middle and no two units areneeded, and on both sides thereof, there are decomposition/oxidationunits of NH₃. A considerable advantage is also to use two identicalunits on both sides of the reduction unit in the reverse flow reactor.In the reverse flow reactor, there can also be conventional heattransfer structures, which are also placed identically on both sides ofthe other units.

According to an object of the invention, oxygen or a substancecomprising oxygen is fed into the fluid and/or the fluid mixture beforethe decomposition/oxidation unit of NH₃ and/or before the selectivereduction unit and/or before the removal unit of laughing gas. Byfeeding the substance comprising oxygen (such as oxygen, air, ozone,hydrogen peroxide), part of the ammonia can be made to oxidize intonitrogen oxides, whereby an NH₃/NO_(x) mixture can be formed. This isadvantageous in objects that otherwise do not comprise sufficientamounts of oxygen for the reactions. In some applications, the flue orprocess gas does not comprise enough oxygen. These objects includegasifying gases, gases releasing/being removed from air-tight sources(such as soil, water). The substance comprising oxygen can be feddirectly to the fluid going to the decomposition/oxidation unit of NH₃only, whereby an especially oxygen-rich mixture is obtained in the unit,promoting the oxidation reaction, in particular.

According to an object of the invention, a reducing agent, such asammonia and/or a derivative of ammonia and/or hydrocarbon or hydrocarbonderivatives are fed into the fluid and/or the fluid mixture before thedecomposition/oxidation unit of NH₃ and/or before the selectivereduction unit and/or before the removal unit of laughing gas. This isan additional advantage, which can be used in some circumstances, ifthere is no other way to provide a suitable mixture in the reductionunit. This can also be an accessory, which is used in certain conditionsonly, when no suitable mixture is obtained (a too low NH₃/NO_(x) ratio)by means of the flow technology or valves. An extra feeding can also beused for quick adjustments from feedback measurements. By addinghydrocarbon, the temperature of the system can be increased as desired.NH₃ can also comprise the same fluid that is to be treated, which hasbeen stored and which is fed for this adjustment, when needed.

According to an object of the invention, the method includes adecomposition/oxidation unit of NH₃, a selective reduction unit and aremoval unit of laughing gas, which are integrated into the same unitand structure. The simplest solution of the method is to integrate theseunits into the same structure. In that case, the by-pass isreaction-technical, while part of NH₃ does not react in the flow orcatalyst channel. In a catalytic application, the integrated system cancomprise a combination of various catalysts. For example, the catalystmay include the said decomposition/oxidation and reduction catalysts ofNH₃. As the NH₃/NO_(x) ratio does not easily remain within a suitablerange, a problem with this solution is its narrow temperature window.

According to an object of the invention, the decomposition/oxidationunit of NH₃ comprises a catalyst that comprises Pt, Pd, Ru or Rh or acombination thereof, and the extent of the by-pass is >70%. Thissolution provided high activities and selectivities in the examples.

According to an object of the invention, the method comprises aselective reduction unit and a removal unit of laughing gas, whichcomprise a catalyst that comprises vanadium, wolfram, copper and/oriron, or a combination thereof. Using these active metals, good resultswere obtained in the method.

According to an object of the invention, the method comprises adecomposition/oxidation unit of NH₃ and/or a selective reduction unitand/or a removal unit of laughing gas, which comprise zeolite, silicondioxide, aluminium oxide and/or titanium oxide. Using these supportmaterials, good results were obtained with the method according to theinvention.

According to an object of the invention, the method comprises one ormore heat transfer stages. Heat exchange is needed to trigger andmaintain the reaction. The reaction heats can be recycled and thereaction started by extra energy, such as fuel feedings.

According to an object of the invention, the decomposition/oxidationcatalyst of NH₃ comprises noble metals, such as Pt, Pd, Rh, Ru, Ag, Ir,Au, base metals, such as Sc, Y, Zr, V, Mn, Cr, Fe, Ni, Co, Zn, Ge, Ga,In, Sn, Ce, or the mixtures or mixed oxides thereof as such or on thesurface of a carrier. These metals have activity in this reaction.

According to an object of the invention, the reduction unit comprisescatalytic material, which comprises base metals Zr, V, Mn, Cr, Fe, Ni,Cu, Co, Ce, W, Hf, Nb, Mo, or the mixtures/mixed oxides thereof as suchor on the surface of a carrier. These metals have activity in thisreaction.

According to an object of the invention, the equipment comprises aremoval unit of laughing gas, which comprises catalytic material thatcomprises noble metals Pt, Pd, Rh, Ru, Ag, Ir, Au, preferably Pt, Pd orRu, or base metals Y, Zr, Mn, Cr, Fe, Ni, Co, or the mixtures/mixedoxides thereof as such or on the surface of a carrier. These metals haveactivity in this reaction.

According to an object of the invention, the equipment comprises, in thedecomposition/oxidation catalyst, the reduction unit and/or the removalunit of laughing gas, a carrier (a support material), which comprisesaluminium oxide, aluminium silicate, such as zeolites, titanium oxide,silicon dioxide, zirconium oxide, silicon oxide, or mixtures or mixedoxides thereof. The purpose of the carrier is to stabilize the activemetals over a large surface area. The carriers used in the tests arenamed in the examples.

According to an object of the invention, the equipment compriseszeolite, which is selected from a group consisting of ZSM-5, ZSM-22,Beta, Y, mordenite, ferrierite, TS-1 zeolites or a mixture thereof. Thezeolites have high surface areas and special pore structures/sizes andacidities, all of which can be utilized in the catalysts of the method.

FIG. 1 shows the method according to the invention, comprising thefunctional units in their general forms or using catalytic units.Accordingly, the units can also function thermally in combustion plants,for example. The by-pass can also be integrated into thedecomposition/oxidation unit of NH₃, whereby the by-pass is a result ofthe fact that part of NH₃ has not reacted (FIG. 2). Part of the ammoniadoes not react, when the coating is omitted from part of the cell in theradial direction. There can also be some uncoated cell at both ends ofthe decomposition/oxidation catalyst of NH₃ to prevent the reactions atthe ends of the cells. Flow-technically, the fluid can also bedistributed through various parts by using effluent splitters (plates,throttlings and/or valves) or by covering part of the face surface ofeither the catalyst or the inert cell. This fine adjustment can be used,if the planned flow distribution, which is implemented by the cellstructures, is not suitable and too much ammonia or, alternatively,nitrogen oxides come to the selective reduction unit. The mixinginterval is essential to allow the fluids, which have passed through thecatalyst and the inert layer, to mix together and to obtain the desiredmixture for the next unit.

The by-pass and the flow control through the various units can also beimplemented by means of flow controllers and feedback from temperature,ammonia and NO_(x) measurements (FIG. 3). The control valves alwaysenable the desired flow distribution through the various units, forexample, on the basis of the temperature or the contents. The uncoatedunit can also be a completely separate structure, whereby there is norisk of reactions on the face surfaces (FIG. 3). In this solution, thecontrol valve can be provided for extra adjustment.

The systems according to the invention can be built in different waysaccording to the object and goals (FIG. 4). Thus, the method cancomprise the decomposition/oxidation unit of NH₃, which can be partlybypassed and, after that, there are the selective reduction unit and/orthe decomposition/reduction unit of N₂O in the direction of flow.

In the reverse flow reactor, the system can comprise adecomposition/oxidation unit of NH₃ on both sides of the reduction unitand/or the N₂O unit (FIG. 4). The reverse flow reactor can also compriseconventional heat exchangers on both sides of the catalyst units. Thereverse flow reactor can be used to exploit the reaction heat, and thereactor operates without extra heating with a relatively small amount ofemissions, the reactions of Which result in larger amounts of reactionheat than energy loss. The heat exchangers employ conventional cellularheat exchanger structures, which endure the operating conditions. Inparticular, the cell structures can be made of metal foil and the formof cells consists of straight and creased foil or two creased cellstructures. The material of the heat exchanger is good in conductingheat and it endures the operating conditions. Typical materials comprisevarious metal plates and foils comprising, among others, iron, chrome,aluminium, nickel, copper and/or cobalt. The heat exchanger can also becoated. The method can also employ combinations of one or more reverseflow reactors and normal tube reactors with one flow direction, wherebythe removal unit of laughing gas can be placed after the reverse flowreactor, for example. The combination of several reverse flow reactorscan be used to maintain different temperatures in the differentreactors, and thus to optimize the operational windows and the energybalances of the system. A combination of several reactors, which havedeviating operation modes or conditions, can also be used in objects,where hydrocarbons and their derivatives are to be removedsimultaneously with ammonia, for example. Extra heat can be provided byelectric or burner heating or fuel feeding. The oxidation/decompositioncatalyst of NH₃ also works as an effective combustion catalyst, whichcan be used to increase the temperature of the system, if a small amountof burning fuel is fed to the fluid. One or more units can be heated orcooled externally. Other additives (oxygen-comprising or reducingcompounds) or extra energy (e.g., plasma for the oxidation) can also beused in the units to improve the oxidation and reduction reactions.

In the method, a reactant (NH₃, NO_(x), N₂O, HCs, oxygen) can also befed to the pipework, for example, in situations, where the requiredconditions cannot be provided otherwise. Oxygen can be fed to theeffluent gases in mixtures that comprise very low amounts of oxygen tooxidize NH₃ in the decomposition/oxidation unit of NH₃. The oxidation ofNH₃ can be implemented by feeding enough oxygen to the low-oxygenmixtures to decompose NH₃, resulting in a mixture with a suitableNH₃/NO_(x) ratio. In the thermally functioning selective reduction unit,NH₃/NO_(x) can be >>1, but in the catalytic reduction unit, a systemwith an NH₃/NO_(x) ratio of slightly less than 1 usually works the best.Thermal applications comprise, e.g., combustion boiler objects, wherethe units can be located inside the boiler itself, comprising certaincombustion spaces in the boiler. In these objects, the selectivereduction unit generally works in accordance with the principles of theselective, non-catalytic reduction. The units according to the inventioncan also be provided after the boiler, whereby the temperatures aresuitable for the catalytic units and the excess amounts of ammonia andnitrogen oxides can be removed.

In power plant boilers or gasification plants, powdery or granularcatalysts can also be fed to the various stages alone or along with thefuel or other substances that are fed to the plants (desulphurizationchemicals, fluidized bed materials, ashes, slag), whereby at suitablepoints, catalytic materials are fed to the decomposition/oxidation ofammonia, the selective reduction and the removal of laughing gas. Thecatalytic materials for the decomposition/oxidation of ammonia and thereduction contain, e.g., iron, calcium, magnesium, zirconium, cerium,titanium, aluminium, silicon and/or carbon. As to its conditions,fluidized bed combustion is favourable to be used in the methodaccording to the invention. The temperature is often fairly low, 800 to900° C., and the feeding of air/fuel takes place in stages, whereby theoxidation of ammonia can take place thermally in the reduction zones, orit can be enhanced by a catalytic material, such as ash or ironcompounds (e.g., the slag or ashes from the metal industry). In thesubsequent zones, the thermal and catalytic reduction of ammonia andnitrogen oxides as well as the removal of laughing gas can be furtherutilized. The first and second units can be thermal and the thirdremoval unit of laughing gas can be catalytic.

In gasification, the decomposition/oxidation unit of NH₃ can be situatedin a pressurized or unpressurized gasification process, and thereduction unit and the laughing gas removal unit can be located outsidethe gasification plant in a combustion plant or after the same. In thegasification processes, there can also be a separate or integratedcatalyst for the purification of hydrocarbon compounds, mainlycomprising the same active components as the removal/decompositioncatalyst of NH₃ according to the invention. In such processes, there canalso be a particle filter provided before the combustion plant thatgenerates energy and/or electricity. In the method according to theinvention, combinations of thermal and catalytic units can also be used.The method can be used in stationary or moving objects.

The N₂O removal unit can also have selective reducing properties(NO_(x)+NH₃→N₂), SCR properties, and the selective reduction unit canhave decomposition properties of N₂O, or these properties are integratedinto the same units. Such catalysts include, e.g., Fe/zeolite catalysts,which have activity both in the decomposition/reduction of N₂O and inthe SCR of nitrogen oxides. Instead of iron, the active component inzeolite can also be another metal that is known to be active indecomposing laughing gas.

The ranges of use of the invention include flue gas and effluent gasapplications in objects, where the mixture comprises oxygen in excessamounts. If the original mixture comprises no oxygen at all or notenough oxygen, it can be added to the mixture before thedecomposition/oxidation unit of NH₃ and before the selective reductionunit. An ammonia reducer or its derivatives or mixtures can also furtherbe fed to the fluid before the selective reduction unit, whereby theNH₃/NO_(x) ratio can be suitably fine-adjusted before the reductionunit. The effluent gases can also comprise other emissions (ammoniaderivatives, hydrocarbons, hydrogen, carbon monoxide, nitrogen oxides),which are removed by the method according to the invention. The othercompounds (ammonia derivatives, HCs, carbon monoxide, hydrogen) can alsoparticipate in the reduction reactions (nitrogen oxides). In oneapplication, gas (usually air) is conducted through soil or liquids, towhich gas ammonia from the soil or air is transferred, and the ammoniacan be treated by the method according to the invention. The method canalso be applied to liquid mixtures comprising ammonia or ammonium.Accordingly, the fluid can also be liquid-based or a mixture of liquidsand gases.

The method can also be applied to other impurities that comprisenitrogen (HCN, HNCO, nitrogen-comprising amides/amines/pyridines, ureaor the derivatives thereof, ammonium compounds), which are to beconverted into harmless compounds, such as nitrogen. In the by-pass,these compounds can partly be converted catalytically into nitrogenoxides that react with unreacted N compounds and form nitrogen. Theeffluent gas can also comprise laughing gas before the method is used.The compounds comprising nitrogen can also be in a liquid phase, wherebythe ammonium compounds, for example, are partly oxidized/decomposed andthe mixture is then conveyed to the reduction unit.

The by-pass according to the invention can be implemented by usingsimilar cell structures both in the oxidation/decomposition unit of NH₃and the by-pass. In that case, the flow is distributed approximately inrelation of the cell's face surface area to the by-pass and the catalystat different temperatures. When using a flow-technical by-pass with adifferent structure, the temperature dependency of the flow in each flowchannel can alter the flow distribution.

The catalyst compositions according to the invention are coated byseparately spraying coating slurry on smooth and creased open metalfoils or surfaces. After the coating, the catalysts are dried andcalcined. Alternatively, the catalyst coatings are coated by dipping orimmersing the finished, generally cellular metal or ceramic catalyststructure in the catalyst slurry. In the manufacture, a combination ofthese manufacturing methods can also be used.

The active metals and promoters have already been added to the slurry orthey have been absorbed into the coated catalyst. The coating and theactive components can also be added from gaseous or solid startingmaterials by means of various methods.

The catalyst coating according to the invention can be pre-coated orpost-coated on normal ceramic or metallic cells or structures, where theform of the hole (e.g., square, triangle), the cell number (10 to 2000cpsi, holes/square inch) or the wall thickness (10 to 2000 μm) can varywithin a wide range, depending on the application. When the effluent gascomprises large amounts of particles or sulphuric compounds, very largecell sizes can be used in the catalyst (<100 cpsi). In objectscomprising a few particles and little sulphur, very small cell sizes canbe used (e.g., >500 cpsi) in the cell. These variable values can alsovary in the same cell or sequential cells, whereby an advantage isobtained because of effective mixing, a low pressure loss or mechanicalstrength, among others. The catalyst structures can be implemented usingpellet-type, extruded or powdery catalysts. The catalyst can also befluidized in a desired spot in a fluidized bed combustion boiler, forexample.

The cell that is to be coated can also constitute a certain type of astatic mixer structure that either comprises mixing zones (e.g., bends,flow barriers or throttlings) in separate channels or the structure ismade by installing creased, corrugated foils or plates one top of theother so that the direction of the wave crest deviates from the incomingdirection of the gas, and the wave crests of the superimposed plates aredivergent. In a conventional metal cell, the wave crests of the creasedfoil are parallel to each other and the main flow direction. The mixingefficiency can be adjusted by varying the angle between the wave crestand the main flow direction. The mixer structure can also be made byalternately folding an obliquely creased foil in an overlapping manner,whereby the wave crests come against each other and not within eachother. The obliquely creased structure can also be rolled up into around roll. In that case, the angle of the oblique crease is small orthe foil is flexible (e.g., from a mesh or perforated). The mixerstructure provides mixing of the flow in the radial direction of thepipe. The mixer structure also provides higher collection efficienciesfor the particles than the conventional cell structure. The shapes ofthe catalysts and the flow channels can be round, elliptical, square,angular, or combinations thereof. Around or inside the reactor, therecan be insulation material and/or heat exchange structures/devices. Thestructure that is to be coated can also partly of fully comprise a wiremesh, sintered porous metal, fibre, or a particle trap.

The catalyst according to the invention can also be coated on two ormore of the above-mentioned catalyst structures that are sequential orparallel in the flow direction. The catalyst structures with the same ordifferent sizes can be situated in the same catalyst converter or theycan be in separate converters, whereby there is a sufficient amount ofpipework between the same. The compositions of the catalysts accordingto the invention, the noble metal charges (such as Pt), the cell numbers(geometrical surface areas) or structures can be mutually similar ordifferent.

The decomposition/oxidation catalyst of NH₃ comprises noble metals (Pt,Pd, Rh, Ru, Ag, Ir, Au) or base metals (Sc, Y, Zr, V, Mn, Cr, Fe, Ni,Co, Zn, Ge, Ga, In, Sn, Ce) or the mixtures or mixed oxides thereof ascatalytically active materials. The surface area and the durability ofthe catalyst can be improved by dispersing the active components aloneor as combinations, for example, on the surface of zeolite, aluminiumoxide, titanium oxide, silicon dioxide, zirconium oxide, metal silicate,or the combinations or mixed oxides thereof (the support material). Anyof the above-mentioned active metals can also function as supportmaterial, on the surface of which the other components are added. Theactive components can form mixed oxides with each other or the supportmaterial. In the decomposition/oxidation unit of NH₃, efforts can bemade to minimize the formation of laughing gas and try to use other thanPt-bearing catalysts, for example. Using Ru, Pd, or PtPd catalysts, theformation of laughing gas can be decreased considerably. Thus, thiscatalyst works as the removal catalyst of NH₃ and the reactions cancomprise the oxidation of ammonia into nitrogen oxides (NO, NO₂), SCRreactions (NO_(x)/NO₂/N₂O+NH₃+O₂→N₂, N₂O+H₂O) or a direct decompositionof NH_(3 (NH) ₃(+O₂)→N₂, N₂O). The N₂ that is formed improves thefunctioning of many SCR catalysts through “a quick SCR reaction”,whereby the activity in the subsequent reduction unit is enhanced.Reducing properties can also be integrated into thedecomposition/oxidation catalyst of NH₃, whereby the catalyst comprisesV or zeolite-based support materials together with the active metalsmentioned above, for example. The catalyst may then comprise, forexample, noble metals in a V-W/TiO₂ catalyst.

The selective reduction catalyst contains, as catalytically activematerial, base metals (Zr, V, Mn, Cr, Fe, Ni, Cu, Co, Ce, W, Hf, Nb, Mo)or the mixtures/mixed oxides thereof. In addition, there can also benoble metals. The surfape area and the durability of the catalyst can beimproved by dispersing the active components alone or in combinations,for example, on the surface of aluminium oxide, aluminium silicates(such as zeolites), titanium oxide, silicon dioxide, zirconium oxide,silicon oxide, or the mixtures or mixed oxides thereof (the supportmaterial). As zeolites, ZSM-5, Beta, Y, mordenite, ferrierite, TS-1 orcorresponding zeolites can be used. The Si/Al₂ ratio of these zeolitesis within 10 and 500, preferably within 20 and 60. The active componentscan form mixed oxides with each other or the support material.

The catalytically active materials in the removal unit of laughing gas(N₂O) comprise noble metals (Pt, Pd, Rh, Ru, Ag, Ir, Au, preferably Pt,Pd or Ru) or base metals (Y, Zr, Mn, Cr, Fe, Ni, Co) or the mixtures ormixed oxides thereof. The surface area and the durability of thecatalyst can be improved by dispersing the active components alone or incombinations, for example, on the surface of aluminium oxide, aluminiumsilicates (such as zeolites), titanium oxide, silicon dioxide, zirconiumoxide, silicon oxide, or the mixtures thereof (the support material). Aszeolites, ZSM-5, Beta, Y, mordenite, ferrierite, TS-1 or correspondingzeolites or their mixtures can be used. The Si/Al₂ ratio of thesezeolites is within 10 and 500, preferably within 20 and 60. The activecomponents can form mixed oxides with each other or the supportmaterial. Typical removal catalysts of laughing gas comprise FE/zeolites(Fe/Beta, Fe/ZSM-5, Fe/Ferrierite) or other Fe, Ni, or Ru-bearingcatalysts on the surface of the oxides or zeolites mentioned above.

The selective catalytic reduction units and the removal units oflaughing gas can partly be located in the same catalytic structure andcomprise the same catalytic materials. In the catalytic unit, thematerials that catalyze these reactions can be mixed together in thesame catalyst bed or they can be separated from one another in differentcoating layers or different parts of the supporting structure. Whenmaking an integrated catalyst of metal foil, a selective reductioncatalyst can be coated on one foil, and the removal catalyst of laughinggas on the other. In that case, the flow channel comprises, in the axialdirection thereof, the removal catalyst of nitrogen oxides/ammonia onone wall and the removal catalyst of laughing gas on the other wall. Forexample, there can be a VW/Ti-based catalyst on one wall and Fe/zeolite(such as Fe/Beta, Fe/ZSM-5) on the other.

The reduction catalyst of laughing gas can also be integrated into theoxidation/decomposition catalyst of NH₃. All three units can also beintegrated together, whereby the catalyst oxidizes part of the ammoniainto nitrogen oxides, and functions as a selective reduction catalyst(NH₃+NO→N₂) and the removal catalyst of laughing gas (N₂O→N₂ orN₂O+NH₃→N₂). The removal of laughing gas can take place by decompositionor reduction by means of ammonia or other reducing agent that is in thefluid or has been added thereto. The decomposition unit of laughing gascan also be placed before the reduction unit in the direction of flow,whereby laughing gas is removed before the reduction unit.

DETAILED DESCRIPTION OF THE INVENTION

The appended examples describe some applications of the invention.

The preparation of the Catalysts Described in the Examples:

Slurry was prepared from raw coating materials, whereto activeingredients and binders were added with a purpose of ensuring theadhesion and the cohesion on the surface of the supporting structure. Asbinders, Si or Al sols were used for the SCR catalysts and Al sol forthe decomposition/oxidation catalyst of NH₃. The prepared slurry wasused to coat 50-μm thick smooth and creased metal foils; the sampleswere dried at about 110° C. and calcined for 4 hours at 550° C. Desiredamounts of Pt, Pd, Ru and V were absorbed into the catalyst using Ptammin carbonate, Pd nitrate, Ru solutions or ammonium vanadate solutionsas starting materials. In that case, the active components are dispersedinto small particles on the surface of the catalyst. After theabsorption, the catalyst was dried at about 80 to 300° C. and calcinedin the air. A cellular sample was provided by rolling together thesmooth and the creased coated foils. The specific surface area of theactive support material on the various samples was about 50 to 300 m²/gafter the preparation. The amount of support material on the surface ofthe metal foil was about 40 to 60 m²/g. In the Pt/Al—Ti—Si catalyst,(No. 1), a Pt-free, thin surface layer was used, whereby, in theoxidation reaction, the entry of active Pt (or other noble metal) to thesubsequent reduction unit is prevented. The decomposition/oxidationcatalyst can thus be coated by an inert support material, which whendetaching and drifting forward, does not affect the activity of thesubsequent reduction catalyst. For example, the composition can have thesame or corresponding activity as the reduction catalyst does.

TABLE 1 Cell catalysts used in activity tests. Active compo- Support ma-nent Cell num- Catalyst terial % in the support ber No. code g/m²material cpsi 1 Pt/Al—Ti—Si 42 + 8 1.2 + 0 Pt 400 2 Pt/Al—Ce—Zr 50 0.9Pt 300 3 1.1Pt/Al—Ce—Zr-ZSM5-Beta 40 1.1 Pt 500 4 Pt/Al—Ce—Zr-ZSM5-Beta50 1.4 Pt 400 5 0.4Pt/Al—Ce—Zr-ZSM-5-Beta 50 0.4 Pt 400 6 Ru/Al—42Ce 400.3 Ru 500 7 Ru/Al—28Ce 40 0.3 Ru 500 8 PtPd/Al—Ce—Zr 42 1.1 PtPd (1:1)500 9 Pd/Al—Ce—Zr 49 1.0 Pd 400 10 Rh/Al—Ce—Zr 61 0.8 Rh 300 11V—W/Ti—Si 50 2.4 V₂O₅ 600 12 Fe/Beta-Al 34 ~1 Fe 600 13 Fe/ZSM-5-Al 34~1 Fe 600 Cpsi = cells per square inch.

The activity of the catalysts was tested in laboratory conditions, whichsimulated effluent gases that contained ammonia and air. The compositionof the inlet of the laboratory reactor was adjusted bycomputer-controlled mass flow regulators, and the composition wasanalyzed by continuous FTIR analyzers, enabling the separation ofvarious nitrogen oxides (NO, NO₂, N₂O) and the ammonia from each other.The conditions in the activity measurements carried out by thelaboratory equipment were as follows:

TABLE 2 Gas compositions used in the laboratory simulation. Compound Mix1 Mixture 2 NH₃, ppm 80 1000 O₂, % 21.8 21.8 N₂ the rest the rest Spacevelocity 50.000 ~25.000-50 000 h⁻¹ over the various units Space velocity(SV) = the rate of flow of exhaust gas/the volume of catalyst cellConversions in the empty reactor were insignificantly low.

EXAMPLE 1

A problem with the noble metal catalysts is their poor selectivity, eventhough it is possible to remove all of the ammonia at over 250° C.(FIGS. 5 and 6). Instead of nitrogen, too much laughing gas, NO, and NO₂were generated. It was possible to decrease the formation of laughinggas by using the Ru catalyst (15% of NO₂ at the maximum) instead of thePt catalyst (30% of N₂O at the maximum), but the selectivity intonitrogen was too low, when using exclusively such well-knowndecomposition or removal catalysts of ammonia.

EXAMPLE 2

The typical SCR catalysts that are used for the removal of nitrogenoxides can also be used for the removal of ammonia in lean conditions(excess amounts of oxygen with respect to the oxidation of ammonia)(FIGS. 7 and 8). The SCR and NH₃ oxidation activities of the SCRcatalyst change as a function of temperature, when feeding ammoniaalone, whereby a temperature window is found, where the conversion intonitrogen was 69% with the V—W/Ti—Si catalyst at 350° C. (80 ppm NH₃) and87% with the Fe/Beta catalyst at 500° C. Accordingly, in the SCRcatalyst, a partial oxidation of NH₃ into NO_(x) (NO/NO₂) and an SCRreaction (NO_(x)+NH₃+O₂→N₂) are combined in the application used. Withthe Fe/Beta catalyst, the formation of laughing gas remained low. Withthe V catalyst, the formation of NO_(x) was low, but too much laughinggas was generated.

EXAMPLE 3

By combining the V—W/Ti—Si catalyst and the Fe/Beta catalystsequentially, the conversion into nitrogen was enhanced and the amountsof both laughing gas and NO_(x) remained low (FIG. 9). The conversioninto nitrogen was as much as 96% at 500° C., whereby all of the ammoniahad been removed and there was 1% of laughing gas, the rest being No andNO₂. By this combination, the selectivities are acceptably high, andthis combination is also well-suited to the reverse flow reactors, asthe catalysts are the same in both flow directions. In this concept, theoxidation/decomposition and the reduction catalysts of NH₃ and theremoval catalysts of laughing gas are integrated.

EXAMPLE 4

By combining the decomposition/oxidation/removal catalyst of NH₃ (Pt orRu catalysts) and the SCR catalyst (V—W/Ti—Si) in series, it waspossible to change the operational window and increase the conversionsinto nitrogen, but the undesired conversions into nitrogen oxidesremained fairly high (FIGS. 10 and 11). By this combination, the bestselectivity into nitrogen is found at low temperatures (<250° C.). Aproblem with high temperatures is the great formation of NO_(x).Accordingly, the oxidation/decomposition catalyst could be used todecrease the operating temperature.

EXAMPLE 5

As the direct combination of the NH₃ decomposition/oxidation catalystand the SCR catalyst did not yield a desired result but an excess amountof NO was generated, the oxidation of NH₃ in the first unit was adjustedby means of a by-pass, where NH₃ should not oxidize at all. In this way,the idea was to obtain in the inlet of the SCR catalyst a mixture ofNH₃:NO_(x)=1, which would react in the SCR reaction. At first, theportion of by-pass was 50%, whereby the conversion into nitrogen at ahigh temperature improved, but a lot of NO was still generated (FIGS. 12and 13). In practice, the operating temperature in this system can besuch that the ammonia is fully removed, but not too much NO is yetgenerated. In that case, conversions of 50% into nitrogen are obtained,Pt/Al—Ti—Si being in the by-pass in the first unit, and conversions of75% into nitrogen, Ru/Al-42Ce being in the by-pass in the first unit.The SCR catalyst was V—W/Ti—Si.

EXAMPLE 6

The catalyst combination was tested with a 65% by-pass, using variousdecomposition/oxidation catalysts of NH₃ together with the VW/Ti—Sicatalyst (FIGS. 14 to 16). Using Pd or Rh catalysts for theoxidation/decomposition of NH₃, it was possible to increase theformation of nitrogen to a level of 72 to 75%, the formation of laughinggas remaining below 20%. By replacing the VW/Ti—Si catalyst with theFe/Beta or V—W/Ti—Si+Fe/Beta catalysts, the formation of N₂ increased to86% and the formation of laughing gas was below 10% (FIG. 16). TheFe/Beta catalyst worked in the combination as the removal catalyst oflaughing gas and also as the selective reduction catalyst.

EXAMPLE 7

By further increasing the portion of by-pass to 86% by means of the Ptcatalyst, the formation of NO₂ increased to 65%, but a rather largeamount of laughing gas is formed by this combination with various Ptcontents (FIGS. 17 and 18). With the Pt catalyst, NH₃ can be removed atlow temperatures (>99% 300° C.), but the formation of laughing gaspresents a problem. By using the PtPd catalyst with the same by-pass andreduction catalyst, the formation of NO₂ increased and the formation oflaughing gas decreased (FIG. 19).

EXAMPLE 8

By adding the Fe/Beta catalyst before and after the VW/Ti—Si catalyst,while the Pt catalyst was bypassed, the formation of N₂ increased toover 70% and it was possible to remove almost all of the laughing gas atover 450° C. (FIG. 20).

EXAMPLE 9

By replacing the Pt catalyst of the previous example with a PtPdcatalyst with the same by-pass, the formation of N₂ could be increasedto 84% and the amount of laughing gas at 400° C. was 11%, disappearingcompletely within 450 and 500° C. (FIG. 21).

EXAMPLE 10

As laughing gas is formed in the decomposition/oxidation catalyst of NH₃even with large by-passes, the portion of gas going through the catalystwas further decreased (FIG. 22). By using a 98% by-pass with the PtPdcatalyst and, thereafter, combinations of Fe/Beta+VW/Ti—Si+Fe/Beta, alevel of about 94 to 97% of the formation of N₂ was reached, the amountof laughing gas in the products remaining below 2%. This combinationworks on the desired level, converting all of the ammonia and formingnitrogen with a conversion of >95%, the amounts of laughing gas, NO, andNO₂ remaining below 2% in the product gas. By using the PtPd catalyst,the amount of laughing gas thus generated can be decreased. It ispossible to even use higher Pt/Pd ratios, whereby the amount of laughinggas thus generated further decreases. In the same way, it is possible touse other metals with Pt.

EXAMPLE 11

By using a Pt catalyst provided with by-passes on both sides of theFe/ZSM-5 catalyst (integrated selective reduction and removal oflaughing gas), it was possible to decrease the formation of laughing gasto below 2% at over 450° C. (FIG. 23). This is an example of the use ofFe/ZSM-5, the integration of the units, and the use of by-pass on bothsides of the reduction units and the removal units of laughing gas. Inthe same way, it would be possible to use the PtPd catalyst in place ofthe Pt catalyst, and the Fe/Beta catalyst in place of the Fe/ZSM-5, andto use a larger by-pass. The by-passes on both sides also simulate theactivity in the reverse flow reactor.

1-26. (canceled)
 27. A method of removing ammonia from oxygen-comprisingfluids, such as effluent, flue or waste fluids, characterized in thatsaid method comprises at least the following stages: part of the fluid(1) is conveyed to a decomposition/oxidation unit (2) and part of thefluid (1) is conveyed to a by-pass unit (3), part of theammonia-comprising fluid (1) is oxidized in the decomposition/oxidationunit (2) of ammonia, the fluid (1H) that was oxidized in thedecomposition/oxidation unit (2) and the fluid (1) that was conveyed tothe by-pass unit are mixed in a mixing unit (4) to form a fluid mixture(1S), and the fluid mixture (1S) is conveyed to a selective reductionunit (5).
 28. A method according to claim 27, characterized in that thefluid mixture (1S) is conveyed to a removal unit (7) of laughing gas.29. A method according to claim 27, characterized in that the ammonia ofthe fluid mixture (1S) is converted into nitrogen (N₂) selectively inthe selective reduction unit (5).
 30. A method according to claim 27,characterized in that the decomposition/oxidation unit (2) of ammonia,the selective reduction unit (5) and/or the removal unit (7) of laughinggas function catalytically and they are coated on the surfaces ofcellular structures that comprise straight, parallel, divergent, and/orwinding flow channels, the structures being made of ceramic, metallic orcatalytic materials.
 31. A method according to claim 27, characterizedin comprising a selective reduction unit (5) and a removal unit (7) oflaughing gas, which have been integrated into the same unit.
 32. Amethod according to claim 27, characterized in that the by-pass isadjusted so that the ratio of NH₃/NO_(x) contents in the mixing unit (4)is within 0.1 and 10, preferably within 0.8 and 1.6.
 33. A methodaccording to claim 27, characterized in that a reducing agent, such asammonia and/or the derivatives of ammonia and/or hydrocarbons orhydrocarbon derivatives are fed to the fluid (1) and/or the fluidmixture (1S) before the decomposition/oxidation unit of NH₃ (2) and/orbefore the selective reduction unit (5) and/or before the removal unit(7) of laughing gas.
 34. A method according to claim 27, characterizedin comprising a decomposition/oxidation unit of NH₃ (2), a selectivereduction unit (5), and a removal unit (7) of laughing gas, which havebeen integrated into the same unit and structure.
 35. A method accordingto claim 27, characterized in that the decomposition/oxidation unit ofNH₃ (2) comprises a catalyst, which comprises Pt, Pd, Ru or Rh, or acombination thereof, and the size of the by-pass is >70%.
 36. A methodaccording to claim 27, characterized in comprising a selective reductionunit (2) and a removal unit (7) of laughing gas, which comprise acatalyst that comprises vanadine, wolfram, copper and/or iron, or acombination thereof.
 37. A method according to claim 27, characterizedin comprising a decomposition/oxidation unit of NH₃ (2), a selectivereduction unit (5), and/or a removal unit (7) of laughing gas, whichcomprises zeolite, silicon dioxide, aluminium oxide and/or titaniumoxide.
 38. Equipment for removing ammonia from exhaust, flue, or wastefluids that comprise oxygen, characterized in comprising at least thefollowing parts: a decomposition/oxidation unit (2) for decomposing andoxidizing the ammonia in the fluid, a by-pass unit (3) for conveying thefluid (1) past the decomposition/oxidation unit (2), a mixing unit (4)for mixing the fluid (1H) that was oxidized in thedecomposition/oxidation unit (2) and the fluid (1) that was conveyed tothe by-pass unit to form a fluid mixture (1S), and a reduction unit (5)for selectively reducing the fluid mixture (1S).
 39. Equipment accordingto claim 38, characterized in that the decomposition/oxidation catalystof NH₃ (2) comprises noble metals (Pt, Pd, Rh, Ru, Ag, Ir, Au), basemetals (Sc, Y, Zr, V, Mn, Cr, Fe, Ni, Co, Zn, Ge, Ga, In, Sn, Ce), orcombinations or mixed oxides thereof as such or on the surface of acarrier.
 40. Equipment according to claim 38, characterized in that thereduction unit (5) comprises catalytic material that comprises basemetals (Zr, V, Mn, Cr, Fe, Ni, Cu, Co, Ce, W, Hf, Nb, Mo) or themixtures/mixed oxides thereof as such or on the surface of a carrier.41. Equipment according to claim 38, characterized in that the equipment(L) comprises a removal unit (7) of laughing gas that comprisescatalytic material, which comprises noble metals (Pt, Pd, Rh, Ru, Ag,Ir, Au, preferably Pt, Pd or Ru) or base metals (Y, Zr, Mn, Cr, Fe, Ni,Co) or the mixtures/mixed oxides thereof as such or on the surface of acarrier.
 42. Equipment according to claim 38, characterized in that thedecomposition/oxidation unit of NH₃ (2) comprises a catalyst thatcomprises Pt, Pd, Ru or Rh or a combination thereof, and the size of theby-pass is >70%.
 43. Equipment according to claim 38, characterized inthat the equipment (L) comprises, in the decomposition/oxidation unit(2), the reduction unit (5) and/or the removal unit (7) of laughing gas,a carrier that comprises aluminium oxide, aluminium silicate, such aszeolites, titanium oxide, silicon dioxide, zirconium oxide, siliconoxide or the mixtures or mixed oxides thereof.
 44. Equipment accordingto claim 38, characterized in that the equipment (L) comprises zeolite,which is selected from a group of ZSM-5, ZSM-22, Beta, Y, mordenite,ferrierite, TS-1 zeolites or a mixture thereof.